disable parallel graph executor by default

paddle/fluid/framework/parallel_executor.cc

@@ -35,7 +35,7 @@ limitations under the License. */
 DEFINE_string(pe_profile_fname, "",
               "Profiler filename for PE, which generated by gperftools."
               "Only valid when compiled `WITH_PRIFILER=ON`. Empty if disable.");
-DEFINE_bool(enable_parallel_graph, true,
+DEFINE_bool(enable_parallel_graph, false,
             "Force disable parallel graph execution mode if set false.");
 
 namespace paddle {